Rheological additives have been widely employed in the formulation of products such as sealants, adhesives and coatings to provide control of sag or slump during and after application. Various organic and inorganic materials such as fumed silicas, carbon blacks, asbestos, castor oil derivatives, organo-modified clays, and other minerals, fibers and organic synthetics such as polyurethanes and polyamides, have provided thixotropic properties to end products, particularly non-reactive products.
As set forth in U.S. Pat. No. 4,778,843 granted on Oct. 18, 1988, polyamide rheological additives wherein the polyamide chain is capped with a monocarboxylic acid containing from 16 to 22 carbon atoms and either an olefinic unsaturation or a hydroxyl group have been found to be effective in thickening non-reactive organic solvent based coating systems.
U.S. Pat. No. 4,670,173 granted on Jun. 2, 1987 discloses oil-soluble compositions that are useful as viscosity modifiers. Such compositions are formed by reacting an acylating product, a polyamine and a mono-functional acid either in the presence of a hydrocarbon solvent or in the absence of a solvent.
U.S. Pat. No. 4,462,926 granted on Jul. 31, 1984 discloses a polyamide thixotrope for unsaturated polyester resins consisting of at least one cyclohexyl amide of a saturated fatty acid which contains at least 10 carbon atoms and at least one oligomeric ester amide having an average molecular weight of from 600 to 3000, a content of carboxylic acid amide groups of from 1.5% to 15% by weight and a content of carboxylate groups of from 2% to 13% by weight.
Copending patent application Ser. No. 336,002, filed Apr. 10, 1989, U.S. Pat. No. 5,075,407 describes polyamides of one type shown in the specification for use as encapsulants during agents melt adhesives.
However, in many systems either the basic components show appreciable reactivity toward such conventional rheological additives or the additives are simply impractical due to inferior performance, cost or the impartation of undesirable side effects. One such system is the one component moisture cured polyurethane sealants. Such sealants are based on urethane prepolymers with reactive isocyanate functionality. The isocyanate groups of these molecules react readily with active hydrogen containing species such as water, primary and secondary amines, hydroxyls, carboxyls and mercaptans. Many of the conventional rheological additives such as fumed silicas, castor oil derivatives and organomodified clays contain one or more types of these active hydrogen groups and therefore cause detrimental effects to the sealant such as interference with cure rate, final physical properties or package stability. Additionally, the additives are often rendered inactive due to the consumption of active hydrogen groups by the isocyanate groups of the urethane prepolymer.
Some existing rheological additives are relatively inert toward isocyanates if dried and employed under anhydrous conditions. However, their use is limited by other factors. For example, the use of asbestos has been essentially eliminated due to its carcinogenicity. Fine particle/high structure carbon blacks are only effective at high concentrations and also render the sealant black in color. Further, various organic fibers are either high in cost, low in efficiency or provide an undesirable appearance to the sealant product.
Still other products or techniques have been employed such as PVC plastisol fusion, but such processes are very process sensitive or labor intensive.
Polyamides of certain types have been shown to impart thixotropy in various resin or solvent systems. However, polyamides typically possess active hydrogen functionality such as amines or carboxylic acids. As set forth in U.S. Pat. No. 4,778,843, recently introduced polyamide rheology modifying agents have hydroxyl functionality. Such active hydrogen containing species react with isocyanates resulting in final product instability, cure impediment, rheology deactivation or other detrimental effects.
A need exists in the art for a rheological additive that overcomes the foregoing shortcomings.